Bridging the gap
Chemistry in theory
and practice
Dr Madeleine Schultz
Why chemistry is special
"...consider how different chemistry is... ...from most other
sciences. Where is synthetic astronomy, in which new stars or
planets are created so their properties can be compared with the
natural ones? Where is synthetic geology, in which different
versions of the earth are made to see whether they are better or
worse than the one we have? ...chemistry remains the leader by
far in its concern with all that is possible in the world, not just that
which is found in nature."
Chemistry Today and Tomorrow: The Central,
Useful, and Creative Science
By Ronald Breslow
What is a mole?
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a small furry animal
Masses of small things
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a very large number of things
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the same number as there are atoms in 12.00 g of
carbon atoms
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atoms consist of protons, neutrons and
electrons
protons weigh 1.673×10−27 kg
neutrons weigh 1.675×10−27 kg
electrons weigh 9.1×10−31 kg
atoms are usually weighed in amu (now
called u)
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1 u = 1.661×10−27 kg
a proton weighs about 1 u
Masses of atoms
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one N atom weighs 14 u
one O atom weighs 16 u
one H atom weighs 1 u
one Pb atom weighs 207 u
Masses of molecules
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one molecule of H2 weighs 2 u
one molecule of H2O weighs 18 u
one molecule of ethanol H3CCH2OH weighs
1x6=6u
12 x 2 = 24 u
16 x 1 = 16 u
46 u
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one molecular unit of NaHCO3 weighs
23+1+12+(3x16) = 84 u
Masses of big things
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most chemistry in a student lab uses
quantities around 1 g
an average person weighs around 65 kg
real things contain a lot of atoms
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how many H atoms in 1 g?
it is useful to have a shorthard for the large
number of molecules you need to have a
mass in that range
Avogadro's number
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the number of things in a mole of those
things
6.022 x 1023
no units
Grains of sand
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a mole of grains of sand is 6.022 x 1023 grains
of sand
total coastline of the world = ca 1 million kilometres, about 36 % is sandy;
average beach width = 50 metres; average beach depth = 12 metres;
assume a volume of 1 mm3 for a grain of sand.
– total number of sand grains on beaches on Earth is about 2 x 1020 ,
which is 1/3000 of a mole
density of silica = 2.6 g/mL; molecular weight SiO2 28 + (2x16) = 60 g/mol
– approximate number of atoms in a grain of sand is 7.8 x 1019, 1/7700
of a mole
– 7.7 mL of sand contains a mole of atoms
exponentials
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a mole of protons weighs:
6.022 x 1023 x 1.673×10−27 kg = 1 x 10-3 kg = 1 g
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Avogadro's number is used for convenience
moves between
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microscopic scale of individual atoms and
subatomic particles
macroscopic scale that can be used in real life
manipulating positive and negative exponents
fractional exponents
logarithms (pH)
Moles of atoms
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how much do they weigh
what do they look like
a mole of sulfur = 32 g
manipulating simple equations
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a mole of silica weighs 60 g, occupies 23 mL
Importance of maths!
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A mole by any other name...
g/mol = gmol-1
mol/L= molL-1 = M
a(b/b) = a
many students are poorly prepared
one mole each of aluminum, copper, iron, and zinc
Moles of molecules
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how much do they weigh
what do they look like
a 500 mL water bottle contains around 28
moles of water molecules
Water and ethanol
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a mole of sugar - a carbohydrate [C(H2O)]6
a mole of grains of sugar would be similar to
a mole of grains of sand
forms of carbon
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graphite
diamond
buckyballs
a mole of carbon always weighs 12 g
H2O: 18 g; 1 g/mL; 18 mL
1 mole ethanol
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Your mole experiment today
1 mole water
CH3CH2OH: 46 g; 0.79 g/mL; 58 mL
a mixture of 18 mL of water with 58 mL of
ethanol is equimolar
76% ethanol by volume!
Bonding
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ionic eg NaCl
covalent eg H2O, sugars
metallic eg Fe, Au
hydrogen eg DNA, protein shape
strengths of bonds
consequences for physical properties
(solubility, melting and boiling point),
reactions, 3D shape
The chemistry of nutrition
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Carbohydrates
simple and complex carbohydrates Cn(H2O)n
fats - long hydrocarbon chains
proteins - chains of amino acids
ethanol
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simple sugars: glucose, fructose, galactose
OH
H2C
OH
O
C
H
H
CH2
C
C
C
OH
OH
HO
fructose
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disaccharides
H
HO
H
H2C
C
HO
HO
H
C
C
O
C
H
C
OH
H
sucrose
Fats
CH3
H2C
O
H
O
H2
C
OH
C
C
OH
C
H
H
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OH
H2C
C
H
HO
polysaccharides - complex carbohydrates
Protein
CH2
H2C
CH2
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long chains (CH2)
if any double bonds are present, unsaturated
cis and trans orientation of double bonds
H2C
CH2
H2C
CH2
H2C
CH2
H2C
CH2
CH2
H2C
H2C
CH2
H2C
CH2
CH2
H2C
O
CH2
O
O
O
H2C
CH
CH2
O
O
H2C
H2C
H2C
H2C
H2C
H2C
H3C
CH2
CH2
CH2
CH2
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CH2
CH2
H2C
H2C
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H2C
CH2
H2C
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H2C
H3C
CH2
CH2
CH2
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a protein is a series of amino acids
there are 20 different amino acids
the order of the amino acids determines the
function of the protein
3D shape is important
Calories = food energy
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when "cold burned" by the body (kcal/gram)
sugars 4
fats 9
proteins 4
ethanol 7
kcal also known as Calories
SI units for energy are joules 1 J = 0.24 cal
Moles of large molecules
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biological molecules such as proteins and
polymers have very large molecular weights
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Moles of gases
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mass depends on which gas it is
water liquid vs gas
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weighs the same, volume is different
Reactions
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use units Da (Dalton) instead of u
1 Da = 1 u
typical protein MW 50 - 100 kDa
1 mole weighs 100 kg!
how much do they weigh
what do they look like
molar mass of butane in experiment today
1 mole of ANY gas at STP occupies 22.7L
correct formulae!
balance
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electrons
charges
atoms
tips for balancing equations
How much do I need?
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MW
no. moles
making sherbert experiment today
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expected number of moles x MW
need to calculate MW of product
need to know molar ratio
Burning petrol
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Yield
makes CO2
how can we know how much?
environmental consequences of driving
Limiting reagent
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making sandwiches
what is left over?
need to know molar ratio
lolly stoichiometry exercise today
Baking soda and vinegar
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experiment today
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Titration
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NaHCO3 + CH3COOH → NaCH3COO + H2O + CO2
check equation is balanced
aqueous solution - sodium and acetate ions
balloon blows up
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Neutralisation
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HO
O
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O
C
O
–
C
C
similar but different
HO
C
C
H
H
OH
citric acid is a "tri-acid"
different stoichiometry to acetic acid
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3NaHCO3 + C3H5O(COOH)3 → Na3C3H5O(COO)3 + 3H2O + 3CO2
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NaHCO3 + CH3COOH → NaCH3COO + H2O + CO2
2
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at the point where colour changes, assume equal
numbers of moles of reagents
MnO4- is "self-indicating"
I made something in my lab
acid plus base gives a salt plus water
two of today's activities rely on this
citric acid vs vinegar
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most indicators are large organic molecules
change colour at a very specific pH
shows "limiting reagent" in a titration
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limiting reagent determines how much
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indicators indicate an excess
C
OH
2
how do I purify it?
how do I find out what it is?
Chromatography
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separation based on properties of molecules
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purify if not too dirty
crystals only grow if the compound is pure
impurities stay in solution
mixtures separate into their components
how do you get the compounds back off?
Characterisation
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each molecule type moves a unique distance
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size
shape
charge
polarity
Recrystallisation
colour
taste
mp
reactions
spectroscopy
Spectroscopy
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the elephant in the box
different amounts of energy give different
types of information
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IR
UV
Xray
NMR
Chemistry is the central science
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helps to understand biology
biochemistry is the chemistry of biological
molecules
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cell walls
enzymes
haemoglobin
physics explains chemistry
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subatomic particles
electronic structure
Thanks
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CQU for hosting this seminar and workshop
Heather, Kathy and Angela for organising
SCIPP and QUT for funding
you for coming